Project Abstract Severe obesity (body mass index [BMI]>35) affects nearly 20 million adults in the U.S. and is twice as common in adults from the lowest socioeconomic strata compared to the highest. Adults with severe obesity are much more likely to have obesity-related comorbidities, poorer quality of life, and shortened lifespans. Randomized controlled trials and observational studies have found that bariatric surgery provides greater weight loss and comorbidity resolution, better quality of life, and longer lifespans as compared with medical weight management strategies. Using Medicaid status as a way to identify lower socioeconomic status (SES), our preliminary data indicate that lower SES patients who undergo bariatric surgery have worse outcomes than higher SES patients. Among all adults who underwent bariatric surgery in Wisconsin from 2011-2014, Medicaid patients had higher rates of emergency department (ED) visits and readmissions within the first year following bariatric surgery. Similarly, our single institution reviews from two academic medical centers in different states found that Medicaid patients had higher rates of ED visits and readmissions within 90 days of surgery. Medicaid patients also lost significantly less weight than did non-Medicaid patients after bariatric surgery. Reasons for these disparities between Medicaid and non-Medicaid patients undergoing bariatric surgery are unknown. Our long-term goal is to develop and implement effective interventions that will improve the health of adults with severe obesity. Our objective in this application is to identify patient and community-level characteristics that are associated with suboptimal 90-day and 1-year outcomes for Medicaid patients who undergo bariatric surgery. To achieve this, we will use a sequential explanatory design, which includes collection and analysis of quantitative data, followed by collection and analysis of qualitative data. This mixed methods research design will allow us to explain and extend the quantitative findings through additional, qualitative studies. We propose the following two Specific Aims: 1) Identify patient characteristics and community-level determinants of health that are associated with suboptimal outcomes for Medicaid and non- Medicaid bariatric surgery patients; and 2) Understand patient and clinical care team perspectives on how patient, provider, and community-level determinants of health influence outcomes for Medicaid vs. non- Medicaid patients who undergo bariatric surgery.